The present invention relates generally to electronic control systems, configurations and processes for electromagnetic pumps and, in particular embodiments, to such systems, configurations and processes for efficient utilization of power and reduction of power consumption requirements in electromagnetic pumps. Further embodiments of the invention relate to electromagnetic pumps which employ such systems, configurations and processes and yet further embodiments relate to infusion devices and, more preferably, implantable infusion devices which employ electromagnetic pumps having such electronic control systems, configurations and processes.
Infusion devices are typically used to deliver an infusion medium, such as a medication, to a patient. Implantable infusion devices are designed to be implanted in a patient""s body to administer an infusion media to the patient at a regulated dosage, over a period of time. External infusion devices may be designed to be portable, for example, to be worn outside of a patient""s body and connected to the patient by a catheter. Other forms of infusion devices are non-portable devices, typically for use in a controlled environment, such as a hospital.
Infusion devices typically include an electromagnetic pump mechanism that is operated to, selectively drive infusion medium to the patient. Various forms of electromagnetic pumps have been developed for use in infusion devices operating in external or implant environments. Examples of such pumps include those described in U.S. Pat. No. 4,594,058 to Fischell; U.S. Pat. No. 4,684,368 to Kenyon; U.S. Pat. No. 4,569,641 to Falk et al.; U.S. Pat. No. 4,568,250 to Falk, et al.; U.S. Pat. No. 4,636,150 to Falk, et al.; and U.S. Pat. No. 4,714,234 to Falk et al.
Typical electromagnetic pump configurations, such as those described in the above-referenced patents, employ a conductive coil coupled to a battery, through control electronics. The coil is selectively energized by the power source and control electronics to create an electromagnetic field which operates on a moveable armature. When the coil is energized, the electromagnetic field causes the armature to move against the force of a spring, toward a stroke position. When the coil is then de-energized, the mechanical spring force returns the armature to the position it had prior to energizing the coil. By moving the armature between its energized stroke position and its return position, a pumping action is accomplished.
In some contexts of use, infusion devices may be operable for an extended period with a limited power supply. For example, battery powered infusion devices may be implanted in or otherwise connected to patients, to deliver medication at controlled intervals over a prolonged period of time. As the battery power supplies have limited capacities, such devices may require multiple replacements of batteries over their operational life. In the case of an implanted infusion device, a replacement of a battery may require the surgical removal of the infusion device. Even with external devices, the replacement of a battery may require specialized tools, parts or skills which necessitate the services of a specialist or trained technician. Thus, a patient requiring a battery replacement may experience inconveniences and costs associated with seeing specialists, while implant patients may further experience the risks, trauma and costs of surgery. Accordingly, there is a demand in the industry for infusion devices which make efficient use of power supplies and, thus, require fewer power supply replacements. This demand is particularly important for implantable devices.
Prior infusion device pumps, such as the P650005 made by Wilson Greatbatch, Ltd., employ capacitor-discharge power control circuits. Such power control circuits include a capacitor that is charged by a battery and discharged to a coil, to power the pump operation. In one representative example, such power control circuits employ a 47 micro-Farad capacitor which is charged at about 16 volts. Each complete discharge of the capacitor delivers an electric power pulse to the coil sufficient to energize the coil and cause the pump to make one complete stroke. The capacitor is fully charged by the battery between pump stokes.
Because a given capacitor charged to a given voltage level produces a fixed amount of power per complete discharge, the pump receives a fixed amount of power independent of the pump""s power needs. However, the power requirements of the pump can vary due to many different factors, such as the formation of partial blockages in the flow path, changes in atmospheric pressure (which may occur, for example, if a patient travels to a high altitude location or swims or dives under water), or changes in the volume of stored infusion medium.
In order to operate the pump under all expected power load conditions, the capacitor size in such prior devices is selected such that the power output per complete discharge is sufficient to operate the pump in the greatest expected power load condition. As a result, sufficient power to operate the pump in the greatest expected load condition is provided to the pump, even when the pump is not operating under the greatest expected load. Such a power discharge at every pump operation, independent of the pump""s power needs, results in a significant waste of electric power.
Accordingly, there is a demand in the industry for electronic power control systems and processes for electromagnetic pumps which provide sufficient power to operate the pump under varying load conditions, but which minimize or decrease power consumption requirements as compared to prior power control systems. There is a further need in the industry for electromagnetic pump configurations which minimize or reduce power consumption requirements as compared to prior pump configurations.
Embodiments of the present invention relate to electric power control systems and processes, infusion devices and pumps for infusion devices which address the above-mentioned industry demands.
Embodiments of the invention relate to electronic control systems and process, infusion devices and pump configurations for highly efficient use of electrical power. Preferred embodiments relate to such power efficient systems and processes for prolonged operational life with a depletable power source, such as, for example, a battery. Several aspects and features of electronic power control systems and processes and pump configurations described herein allow reduced or minimized power consumption requirement for a given infusion output volume. Various embodiments of the invention include one or more of such aspects and features for improved power consumption efficiency.
Preferred embodiments of the invention relate to electronic control systems and process, infusion devices and pump mechanisms configured for implantation in a patient""s body. Further preferred embodiments employ power consumption efficiency aspects and features referenced above to provide improved operational life within an implant environment.
Yet further preferred embodiments relate to such devices and pump mechanisms configured to deliver relatively precisely controlled volumes of infusion medium, within a relatively wide range of volumes, including relatively small volumes.
Yet further preferred embodiments relate to such devices and pump mechanisms configured to deliver sufficiently precise volumes of relatively high concentration infusion medium.
An infusion device according to an embodiment of the invention includes a generally disc-shaped housing made from a biocompatible material. The housing contains a reservoir for holding a volume of infusion medium, such as, but not limited to, a medication to be administered to the patient. The housing has an outlet through which the infusion medium may be expelled. The reservoir is coupled in fluid flow communication with the outlet.
The infusion device also includes or operates with a pump mechanism coupled in fluid flow communication with the reservoir. The infusion device further includes or operates with an electronic power control system for controlling and providing electronic power to the pump mechanism.
A pump mechanism, according to preferred embodiments, employs electromagnetic and mechanical forces to move between retracted (or quiescent) and forward states, to cause infusion medium to be drawn from the reservoir, through an inlet and forced out of an outlet. A preferred pump configuration includes a housing containing an electrical coil disposed within a core or coil cup made of magnetizable material, a piston extending through an axial channel in the coil and coil cup, an armature disposed at one end of the axial channel and an outlet chamber with a valve assembly disposed at the other end of the axial channel. Other suitable pump configurations may be employed in other embodiments.
In the quiescent state, the piston and armature are urged toward a retracted position. When the coil is energized, an electromagnetic field generated by the coil draws the armature toward the coil cup. As a result, the armature and piston move to a forward stroke position. The movement of the piston between retracted and forward positions creates pressure differentials within the internal chambers and volumes of the pump device, to draw infusion medium into the inlet and drive medium out the outlet.
A power control system, according to preferred embodiments of the invention, is configured for highly efficient use of electrical power by the pump mechanism. According to one preferred embodiment, a power control system comprises a capacitor circuit having a capacitor which is controlled to partially, but not fully, discharge to provide a power pulse to a pump coil. In this manner, the capacitor remains partially charged and need not be re-charged from a fully discharged state. In addition, the power applied to the coil in a given discharge pulse signal may be controlled to correspond to the power needs of the pump, by controlling the degree to which the capacitor is discharged to produce the pulse signal.
According to a further preferred embodiment, the power control system has a power cut-off switch to control the discharge of the capacitor such that the capacitor is stopped from discharging prior to the actual end of the armature stroke. In yet further preferred embodiments, the time at which the capacitor discharge is stopped is selected such that energy remaining in the coil after the capacitor stops discharging is sufficient to continue the movement of the armature to the actual end of the armature stroke. The time at which the capacitor discharge is cut off may be based on the location of the armature in its stroke motion. According to one embodiment, electromotive force (EMF) generated in the coil is monitored to determine a suitable time to stop discharging the capacitor. According to a further embodiment, a suitable time to cut off the capacitor discharge is pre-selected and set, based on observed pump operations at various capacitor shut-off times.
According to yet further preferred embodiments, a power disconnect switch is provided between the capacitor and the battery, to allow the capacitor to be electrically disconnected from the battery during storage or other periods of non-use. In this manner, the system may avoid losing battery power due to the inherent leakage of the capacitor during prolonged periods of non-use.
In yet further preferred embodiments, a detector is provided to detect the pressure differential between the inlet and outlet of the pump mechanism and the power control system adjusts the power applied to the coil based on the detected pressure differential, for example, by controlling the capacitor shut-off time. In this manner, the power control system may apply more power, for example, by providing a longer capacitor discharge period when the detected pressure differential increases, and less power or a shorter discharge period when the detected pressure differential decreases. In further preferred embodiments, a detector is provided to detect the battery voltage and the power applied to the coil by the power control system is adjusted based on the detected battery voltage. In this manner, the power applied to the coil may be reduced to conserve battery life, for example, by reducing the capacitor discharge period, as the battery voltage level decreases.
According to further preferred embodiments, the pump mechanism includes one or more features relating to structural configurations for improved power consumption efficiency. Such features include pole configurations, where the ratio of the surface areas of inner and outer pole surfaces is selected to improve power consumption efficiency. Another feature comprises pole interfaces which provide a gap between the outer pole surfaces that is greater than a gap between the inner pole surfaces, where the ratio of the gaps of inner and outer pole surfaces is selected to improve power consumption efficiency. Another feature comprises the aspect ratio of the coil which may be selected to improve power consumption efficiency. Yet another feature comprises an armature configuration with magnetically conductive material forming radial flux paths and fluid passages therebetween, where the fluid passages reduce fluidic resistance as the armature is moved during a pump stroke. Yet another feature comprises an armature configuration with magnetically conductive material forming radial flux paths without fluid passages therebetween.
Another manner of improving the operational life of an infusion device according to embodiments of the invention is to reduce the number of operations of the drive mechanism required over a given period of time, by pumping reduced volumes of a higher concentration infusion medium (an infusion medium with a higher concentration of active ingredients) or pumping higher concentration volumes at reduced intervals. Accordingly, a number of aspects and features relating to the power control system and pump mechanism described herein can provide, or be combined to contribute to the efficient use of power, to, thereby, prolong the operational life of an electromagnetic pump mechanism.
These and other aspects and advantages of the invention will be apparent to one of skill in the art from the accompanying detailed description and drawings.